Differential transmissions are used to convert input motions to output motions changing the axes of rotation. Typical differentials utilize bevel gears in a complex assembly that generates significant bearing radial and thrust loads reacted through shafts cantilevered from bearing supports. These approaches are susceptible to backlash and are typically limited to two inputs and two outputs.
In robotic and advanced mechanism applications, differential mechanisms are often used to provide compact multijoint actuation and are either actuated directly by distributed motors or remotely via cables. Cable actuation reduces system weight but adds significant complexity to cable handling and reduces stiffness. Direct drive differentials are complex and heavy, burdened with large bearings for each rotating component to handle the reaction loads generated in the mechanism. Extremely precise gearing and components are required to keep backlash at a minimum, and direct drive and cable driven differentials are typically limited to two axes of motion.
Typical differential mechanisms are those devices disclosed in the following U.S. Patents:
______________________________________ U.S. Pat. No. Inventor(s) Issue Date ______________________________________ 4,512,710 Flatau April 23, 1985 4,684,312 Antoszewski et al. August 4, 1987 4,704,065 Allared November 3, 1987 4,842,474 Torii et al. June 27, 1989 4,921,293 Ruoff et al. May 1, 1990 4,976,165 Nagahama Dec. 11, 1990 5,151,008 Ishida et al. Sept. 29, 1992 5,187,996 Torii et al. February 23, 1993 5,197,846 Uno et al. March 30, 1993 5,201,239 Bundo et al. April 13, 1993 5,207,114 Salisbury, Jr. et al. May 4, 1993 5,231,889 Lee et al. August 3, 1993 5,249,479 Torii et al. October 5, 1993 5,697,256 Matteo Dec. 16, ______________________________________ 1997
The devices disclosed in the above-identified patents are actuated via distributed direct motor actuation or remote cable actuation and most are limited to two axes of motion. The advantages and disadvantages of which are addressed above. More specifically U.S. Pat. No. 5,207,114 is an example of a whole arm manipulator which utilizes remote actuation through a four axis cable driven differential. The manipulator utilizes a complex array of cables and pulleys providing all speed reduction and differential action. The system is extremely difficult to assemble and maintain and is impractical for reliable robotic service. U.S. Pat. No. 5,697,256 is an example of a Hybrid Differential Transmission which utilizes a combination of planetary input gearing and cable output to achieve a compact two-axis differential. This design does not eliminate backlash and utilizes bearings to support all rotating components.
Therefore, it is an object of this present invention to provide a triple epicyclic differential transmission which converts three parallel input motions to three orthogonal output motions.
It is yet another object of the present invention to provide a triple epicyclic differential transmission which utilizes a combination of planetary gear drives and cable drives.
Moreover, it is another object of the present invention to provide a triple epicyclic differential transmission which is designed to provide zero backlash and zero thrust loads.
Further, it is an object of the present invention to provide a triple epicyclic differential transmission which provides a large ratio of cable to pulley diameter, and temperature and wear compensation.
It is yet another object of the present invention to provide a triple epicyclic differential transmission which includes a large opening through the center for accommodating signal wires.
It is also an object of this present invention to provide a triple epicyclic differential transmission wherein a plurality of the transmissions can be combined for a variety of purposes.
Further, it is an object of this present invention to provide a triple epicyclic differential transmission wherein output joints can be locked thereby reducing the number of axes while maintaining all the advantages of the invention.